In one technology, there is known a sensor device in which a minute differential output voltage output from an output amplifier circuit having an instrumentation amplifier equipped with an offset adjustment function or from an acceleration sensor is amplified by the output amplifier circuit having the instrumentation amplifier.
Also, for example, PLT 1 discloses a sensor device that uses an output amplifier circuit having an instrumentation amplifier (i.e., amplifier for instrumentation) which amplifies a minute deviation voltage output from an acceleration sensor or the like, and an output amplifier circuit having an offset voltage adjustment circuit.
FIG. 1 is a circuit configuration view illustrative of an output amplifier circuit, in one technology, described in JP 2006-174122 A, and the sensor device that uses the output amplifier circuit. The output amplifier circuit uses the sensor technology of the variable resistance that converts a predefined physical quantity such as a piezoresistance into the resistance value. A resistance change of the variable resistance is converted into a voltage signal by a Wheatstone bridge circuit 20, and signals are amplified by an instrumentation amplifier 50.
In other words, an acceleration sensor 10 is configured with the Wheatstone bridge circuit 20 connected between the ground and a reference voltage input terminal 11 to which the reference voltage VREF is input. The Wheatstone bridge circuit 20 includes four piezoresistance elements 21 to 24 to detect a resistance change as a change in the bridge output voltage, and then outputs differential output voltages VIP and VIN to an output amplifier circuit 30.
In addition, the output amplifier circuit 30 has an instrumentation amplifier 50 configured with an offset voltage adjustment circuit 40 and operational amplifiers 51 to 53. The output amplifier circuit 30 further includes a first input terminal 31 to which the differential output voltage VIP is input, a second input terminal 32 to which the differential output voltage VIN is input, a first voltage input terminal 33 to which an offset voltage VOFFIN is input, a second voltage input terminal 34 to which a reference voltage VCOM, of the output from the instrumentation amplifier, that is a ½ voltage level of the reference voltage VREF, a reference voltage input terminal 35 to which the reference voltage VCOM is input, an output terminal 36 from which an amplifier circuit output voltage VOUT is output, an offset voltage adjustment circuit 40 with an output side being connected to the input terminal 33, and the instrumentation amplifier 50 with an input side being connected to the input terminals 31 to 34.